Other stanzas of ten lines are a b a b b c d c d5 d6, a b b a c d d c e5 e6, a b a b c c d e e5 d6.
In this figure, b c is one third longer than a b, and c d than b c; and so on.
A B is the axis of the terrella and of the orbes, c d the quator.
The curve should be so far continued as that h f shall be to c d as c d to a b.
First draw the two lines a b and c d at right angles, intersecting at the exact centre.
The drawbridge is a piece of stiff paper hinged to c d, and has match sticks gummed across it.
Let a b' d' c be the shape of the figure after five hours' motion; then the line a b would be extended to a b' and c d to c d'.
It is kept in its place by a piece of paper, c d E, which is gummed to cover and also to the cork.
The distance, c d, between the foot of this perpendicular and the other edge is the length of a wave of the light.
It is well to begin by sawing along lines a b and c d in Fig. 387, to roughly shape out bow.